Autonics BFC Series, User Manual

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1 Modbus RTU protocol
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1.8 Exception Response-Error Code
If occurs an error, send a response command and transmit each Exception Code after set(1) the
highest-level bit of received command(Function).
Slave Address
Function
+80 H
Exception Code
Error Check(CRC16)
Lo(Lower) Hi(Upper)
1Byte 1Byte 1Byte 1Byte 1Byte

ILLEGAL FUNCTION (Exception Code: 01 H): A command that is not supported.

ILLEGAL DATA ADDRESS (Exception Code: 02 H): Starting address of queried data
is inconsistent with transmittable address from the device.

ILLRGAL DATA VALUE (Exception Code: 03 H): Numbers of queried data are
inconsistent with the numbers of transmittable (transferable) data from the device.

SLAVE DEVICE FAILURE (Exception Code: 04 H): Not properly completed the
queried command (order).
If reading the output status of non-existing coil 001001(03E8 H) [ON: 1, OFF: 0] on
Slave(Address 17) from Master.

Query (Master)
Slave Address Function
Starting Address No. of Points Error Check(CRC16)
Hi(Upper) Lo(Lower) Hi(Upper) Lo(Lower) Lo(Lower) Hi(Upper)
11 H 01 H 03 H E8 H 00 H 01 H ## H ## H

Response (Slave)
Slave
Address
Function
+80 H
Exception Code
Error Check(CRC16)
Lo(Lower) Hi(Upper)
11 H 81 H 02 H ## H ## H
CRC16